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Studies on drilling predation in the fossil record often analyze site stereotypy and drilling frequency. Postmortem prey shell breakage can create particular problems for these analyses, especially in high-spired gastropods (e.g., normalizing drill hole location and estimating the number of individuals in a sample). As a result, many previous studies of these taxa have considered only “complete specimens” though “completeness” is rarely well defined, thereby frequently excluding much potential data. We applied two approaches to collect predation data from incomplete shells of Turritella alumensis from the Pliocene Jackson Bluff Formation in Florida. First, we studied site stereotypy using a Theoretical Apex System to normalize drill hole location. Including incomplete specimens revealed a different pattern of site stereotypy than some previous authors have noted: we found two potential populations of drillers acting on different portions of the shells. Second, we calculated drilling frequency by creating a new calculation for normalizing the minimum number of individuals of high-spired gastropods within a sample, making it possible to compare samples with variable amounts of shell breakage. The calculated drilling frequency for shells drilled by larger predators generated using this method was consistent with that calculated using only “complete” specimens. Additional studies are needed to determine whether drilling frequencies calculated using “complete” specimens are always consistent with those generated using the minimum number of individuals method introduced here.
Gastropod drilling predation in the fossil record is prevalent and has been documented by many workers; however, vivid documentation of confamilial naticid predation is poor. Here, data compiled from previously published sources, supplemented by unpublished museum collections, document different aspects of naticid confamilial predation (NCP) in a temporal-latitudinal context. Confamilial drilling frequency (DF) showed a Cretaceous low, a small rise to a stable plateau in the Eocene, followed by a peak in the Oligocene, and finally a drop to a stable level from the Miocene to the Holocene. The stepwise rise in DF is comparable with the overall history of drilling predation. However, the temporal increase in DF was visible only in the mid-latitudes, while in other latitudes, no temporal trend was observed. The frequency of failed attack has always been very low. In comparison, a decrease in prey effectiveness (PE) was observed in the Neogene relative to the Cretaceous and Paleocene–Eocene intervals. In case of site selectivity, either apertural or abapertural sites were targeted until the Oligocene, and subsequently became more random. Some of these trends may be biased based on insufficient site selectivity data as well as uneven sampling from different latitudes representing different time intervals. More data on quantification of predation intensities along with the behavioral aspects of NCP are required to properly document other aspects of this interaction.
In order to interpret fossil and sub-fossil associations of vertebrates, it is important to understand how carcasses degrade in nature. Here we describe the process of bone loss from of 32 carcasses from eight species of terrestrial mammals over two to 63 months in two Mediterranean ecosystems in the southwest of the Iberian Peninsula. The carcasses ranged in mass from 5 kg to over 450 kg. These data allow the quantitative description of the dynamics of degradation in three time phases defined by changes in the rate of bone loss as measured by the Skeletal Conservation Index (SCI). The SCI values estimated for each phase of degradation is considered the fossil potentiality of the carcass. In the first phase, very few bones were lost, followed by a phase of high bone loss driven by scavengers. The rate of bone loss reduced greatly again in the final phase, which was driven primarily by abiotic, environmental factors. The largest carcasses spend a longer time in each phase, and also had a higher SCI at the end of Phase II. The smallest carcasses experienced a much higher variance in degradation, had significantly lower SCI, and many of the smallest carcasses were consumed completely in a short period of time. Differences between localities were observed regarding SCI values. Presence or absence of tree coverage in the place where the carcass was located also had a significant effect on SCI. These data highlight the importance of considering the contemporaneous scavengers when interpreting animals from paleontological contexts. These data also explain the bias observed in many ancient sites whereby larger animals are over represented.
The upper Monongahela and lower Dunkard groups of southeastern Ohio include abundant paleosols containing ichnofossils as well as vertebrate, invertebrate, and plant body fossils. These paleosols formed on diverse Late Pennsylvanian to Early Permian landscapes in an alluvial setting. This study investigated small-scale lateral and vertical variability of the paleosols that formed at the distal edge of the Dunkard Basin. Three detailed, 32-m thick stratigraphic sections across a 70 m outcrop were measured in eastern Athens County, Ohio. Seven pedotypes representing soil formation in nine subenvironments were identified through bulk geochemical, clay mineralogical, and petrographic analyses as well as a detailed study of the ichnofossils, body fossils, and macromorphological paleosol properties. Ichnofossils were abundant and included rhizoliths, actively to passively filled burrows, and coprolites. These ichnofossils were produced by various plants, larval and adult arthropods, and micro- to macro-vertebrates. Body fossils within the paleosols included micro- and macro bone fragments and teeth, compression plant fossils, ostracodes, and gastropods. Vertical transitions among the subenvironments were due to both fluvial channel migration and climatic changes. Precipitation was seasonally distributed with a range of mean annual precipitation (MAP) from 300–1000 mm/yr through the section. This study demonstrates that by investigating the small-scale lateral and vertical variations in paleosols, finer resolution paleoclimatic, paleoenvironmental, and paleoecological reconstructions are possible.
The genesis of nummulite banks remains a poorly understood topic and the aim of this work is to shed light on it by observing the hydrodynamic behavior of selected larger foraminifera collected from both bank and non-bank deposits. Entrainment and settling velocity of both recent and fossil larger foraminifera were measured using a flume channel and settling tube. Both velocities give information about the reaction of foraminiferal shells to different hydrodynamic conditions affecting their capability to build bank-like sedimentary structures. To assess entrainment, experiments were performed on different substrates to simulate bed load transport on smooth surfaces, fine sand, coarse sand, and bioclastic substrates. Thirty-four recent and 49 fossil shells of foraminifera were used; recent taxa used are Operculina ammonoides, Heterostegina depressa, and Palaeonummulites venosus and fossil taxa used are Nummulites perforatus, N. fabianii, and N. tavertetensis (only A forms were used in this study). Our results seem to differentiate the hydrodynamic behavior of shells collected from banks from those collected from non-bank deposits. The latter possess settling velocities significantly lower than their entrainment velocities, while for taxa collected from nummulite banks, settling velocities are always close to entrainment velocities. Therefore, the relation between hydrodynamics and shape and size may explain why modern larger foraminifera, consistently of smaller size than fossil forms, cannot produce banks and that transport as bed load in moving water was possibly the main trigger for the production of nummulite banks.
Fossils of mosasaurs, late Cretaceous marine reptiles, are frequently found partially preserved in concretions (i.e., hard mineral masses), but little is known about this mode of fossilization. Concretionary fossils are difficult to extract, so are often ignored in the field and laboratory. Accounts suggest that skulls, the most taxonomically diagnostic element, are most often preserved in concretions. The presence of concretions was documented in four anatomical regions (head, torso, tail, limbs) in 48 mosasaur fossils from the Pierre Shale of South Dakota. Specimens were compiled from a restricted lithostratigraphic interval to minimize the effects of lithologic variation on concretion formation. In this sample, the skull and torso were preserved more often in concretions than were limbs and tails. The occurrence of concretion formation was found to vary depending on anatomical region. The results suggest that concretion growth begins in the core of the organism with a higher volume of organic matter, and successively precipitates towards the periphery. The skull and torso contain many taxonomically diagnostic features; thus concretionary specimens should not be overlooked. Additionally, increased likelihood of preservation of specific anatomic regions was dependent on concretion formation, suggesting that our view of the fossil record is affected by concretions.
Nesting behaviors of extant vertebrates can serve as taphonomic models for interpreting extinct archosaurian reproduction. Past studies have examined birds with open nests and nest-bound young and tortoises with buried nests and precocial young. Here we taphonomically describe nesting sites of two crocodylians, American crocodile (Crocodylus acutus) at Turkey Point, Florida and broad-snouted caiman (Caiman latirostris) from Santa Fe and Chaco provinces, Argentina. Surveys focused on eggshell abundance, orientation, and distribution and nest modification of successfully hatched nests. American crocodiles excavate triangular or semi-circular depressions into their nest during hatching. Maximum depths of these parent-assisted hatching traces ranged from 20–45 cm, with a breadth of 50–80 cm. Eggshell orientations outside these excavated pits favored concave down (53.1–80.0%). Broad-snouted caiman constructed mound nests of predominantly plant debris in forested areas with organic rich soil or on vegetation islands. Nests ranged in diameter from 1.2–1.6 m with a height of 0.3–0.6 m. Eggshell orientations within opened egg chambers favored concave up (61.8%), whereas fragments outside the chamber were nearly evenly distributed (51.8% concave-up). Eggshell distribution and orientation at these nesting sites result from adult females assisting and transporting eggs and young during hatching. Observed eggshell orientations in and around the egg chamber in caiman nests are similar to the 60:40 up:down hatching ratio reported in both bird and tortoise nests, whereas crocodile nests are more similar to a 40:60 ratio of trampled shell. Documentation of these nest characteristics and eggshell orientations may facilitate interpretations of parental assistance in the fossil record.